A control method for a variable volume pump is known in which, instead of an ordinary bleed control for controlling a hydraulic actuator speed by changing a bleed flow rate according to an operation amount of a control valve, a directional control valve of a closed center type is used, while a virtual bleed opening is set in the control valve and an area of the bleed opening (virtual bleed opening area) is changed according to the operation amount. According to the control method, a necessary pump discharge pressure is calculated using the virtual bleed opening area and a virtual bleed amount derived therefrom to perform the pump control such that the pump discharge pressure is implemented.